Hi!
> > > + case SNAPSHOT_ATOMIC_RESTORE:
> > > + if (data->mode != O_WRONLY || !data->frozen ||
> > > + !snapshot_image_loaded(&data->handle)) {
> > > + error = -EPERM;
> > > + break;
> > > + }
> > > + down(&pm_sem);
> > > + pm_prepare_console();
> > > + error = device_suspend(PMSG_FREEZE);
> > > + if (!error) {
> > > + mb();
> > > + error = swsusp_resume();
> > > + device_resume();
> > > + }
> >
> > whee, what does the mystery barrier do? It'd be nice to comment this
> > (please always comment open-coded barriers).
>
> Pavel should know. ;-)
Pavel does not known. That memory barrier should be part of assembly
parts, anyway, and AFAIK it is. Should be safe to kill.
> > > + case SNAPSHOT_GET_SWAP_PAGE:
> > > + if (!access_ok(VERIFY_WRITE, (unsigned long __user *)arg, _IOC_SIZE(cmd))) {
> > > + error = -EINVAL;
> > > + break;
> > > + }
> >
> > Why do we need an access_ok() here?
>
> Because we use __put_user() down the road?
>
> The problem is if the address is wrong we should not try to call
> alloc_swap_page() at all. If we did, we wouldn't be able to return the result
> and we would leak a swap page.
I think you need to watch for failing put_user and free the page at
that point. Anything else is racy as __put_user() may fail.
Pavel
--
Thanks, Sharp!
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